1. Field of the Invention
This invention relates to machine tools and more particularly to an automatic workpiece handling system including a machine tool, an automatic workpiece loader for the tool, automatic workpiece positioning means and an automatic completed workpiece unloader.
2. Prior Art
In recent years automated machine tools have become widespread. A particularly successful automation has occurred in connection with high speed turret punches. These punches include relatively large devices having upper and lower spaced apart tool carrying turrets which are maintained in position adjacent a workpiece supporting worktable. The worktable may be equipped with workpiece gripping members which are capable of moving a workpiece in both an X and Y axis with respect to a work station of the turrets. Both the workpiece gripping members and the turrets are controlled from an automatic control center, either a tape read system or a computer such that once a workpiece is properly positioned in the workpiece gripping members and the members properly positioned with respect to the work station, the machine tool can perform a large number of sequential punching operations on the workpiece at precisely determined positions. Upon completion of the desired sequence of punching operations (piece program), the gripping members are normally programmed to return the completed workpiece to a position on the worktable which facilitates unloading of the completed workpiece and loading of a new workpiece.
As such automated turret punches become increasingly improved, it has become practical to operate them totally unattended from the time of initial loading and positioning of the workpiece until completion of the piece program. However, loading, positioning and unloading of successive workpieces remains a manual operation which both adds an unnecessary cost to the manufacture of a large number of identically punched parts while at the same time reduces the manufacturing speed attainable.
Therefore, it would be an advance in the art to provide some construction embodying a machine tool such as a turret punch which was capable of automatically self-loading and unloading. However, due to the criticality of positioning of the workpiece with respect to the work station of the machine, it has not heretofore been practical to contemplate automatic loading devices. Additionally, because of the size of the workpiece will vary from production run to production run, normal product handling systems are not adaptable to automatically load machine tools. An additional factor which works against any attempt to provide an automatic load system results from the fact that machine tools, and particularly turret punches, work with large, unwieldy and heavy workpieces. For example, presently available standard turret punches can handle mild steel sheets on the order of 40" by 96" by 1/4" having a weight per sheet of approximately 270 pounds. A more popular size of workpiece may involve sheets on the order of 40" by 60" of 10 gauge mild steel which would weigh on the order of 100 pounds a sheet.
Because of the common usage of such awkward sheet sizes and the weight thereof, it has previously been suggested to provide loading assistance devices. Such prior devices have normally involved constructions which would assist the worker in lifting or dragging a workpiece onto the machine wool worktable. One such prior art device included pneumatic sheet attaching means attached to cables which terminated at a position overlying a portion of the worktable. While such devices have heretofore been useful in assisting in loading large, uniform sized, workpieces, they have neither been automated nor adaptable to varying workpiece sizes.
Additionally, such prior art loaders have not functioned as time saving devices in that upon placing the workpiece on the worktable, the workpiece still had to be moved into the proper position with respect to the workpiece gripping members and the workpiece positioning side gauge. Additionally the operator had to raise and lower the side gauge and open and close the workpiece grippers before the piece program could be initiated.
Prior art automatically controlled machine tools utilize workpiece gripping members which are movable in an X and a Y direction with respect to the work station centerline. The control device keeps track of the position of the workpiece gripping members and can therefore be said to know the position of the workpiece with respect to the work station once the workpiece has been properly initially positioned and clamped in the gripping members. This initial positioning has normally been accomplished by causing the gripping members to move over the worktable to an initial load position which is known within the controller as the X and Y axis base line or 0 position. The workpiece is then placed on the table in front of the gripping members and the gripping members are cycled to an open position. Since the workpiece is generally rectangular having at least one pair of right angle adjacent sides, positioning, or gauging, is accomplished by moving the front edge of the workpiece backwards into the open grippers until that edge bottoms in each of the grippers. The workpiece is then moved sideways in the grippers until its side edges adjacent the front edge received in the grippers, encounters a fixed abutment precisely positioned on the worktable. The abutment is normally manually projected above the table surface. At this point, with the front edge bottomed in the grippers and the side edge abutting the side gauge projection, the positioning of the workpiece is determined and in view of the control's knowledge of the positioning of the grippers, the control can now be said to have knowledge of the positioning of the workpiece. The grippers are then manually closed and the side gauge manually lowered.
Upon completion of the piece program, it has been known in the art to have unloading assists which, in the manner of the loading assists, grab the completed workpiece and drag it off of the worktable. However the prior art had not been able to automate such devices and relied upon the operator to assure that the workpiece was free of obstruction by elements of the machine including the gripping members and to initiate actuation of the unload assist.
Thus, although the actual sequencing of the workpiece through the punching operation, the selection and alignment of the punches and termination of the operation were all automated, the art has not been able to eliminate the necessity for a full time operator who is required to move the workpiece onto the table, whether assisted or unassisted by machinery, to align the workpiece with respect to the machine in both the X and Y axis, to secure the aligned workpiece to the workpiece gripping members, to clear the workpiece side gauge, to initiate the piece program cycle, to disengage the workpiece from the gripping members, to clear the workpiece from obstruction by the machine and to remove the workpiece from the workpiece table whether assisted or unassisted by machinery.
It would therefore be an advance in the art to provide a substantially completely automated machine tool assembly having means for: isolating a workpiece from a workpiece storage, moving the isolated workpiece to the machine tool worktable, gripping the workpiece by the workpiece gripping members, gauging the workpiece in both the X and Y axis, sequencing the workpiece and the machine tool through the piece program of the machine tool for that workpiece, disengaging the workpiece from contact with the machine tool and unloading the workpiece from the machine tool worktable to a finished product storage area and repeating the sequence without any intervening operator assistance.